Polyether polyols are known to be useful in the production of rigid polyurethane and polyurethane-polyisocyanurate foams. In one of the most common methods for the production of these polyols, a polyhydric alcohol such as sucrose is reacted with an alkylene oxide such as ethylene oxide or propylene oxide in the presence of an alkaline catalyst such as sodium hydroxide. Prior to use in the production of foams, any alkaline catalyst present in the polyol must be neutralized and/or removed to ensure that the catalyst will not interfere with the reaction between polyol and another reactive material such as a polyisocyanate. This is generally accomplished by addition of an acid to neutralize the alkaline catalyst. This neutralization frequently results in the precipitation of a solid salt in the polyol which salt may be removed by filtration. The removed solid is commonly called the filter cake. Traditionally, sulfuric acid has been used to neutralize polyols.
U.S. Pat. No. 4,430,490 discloses a process for producing a polyether polyol from a polyhydric alcohol in which the alkaline catalyst is neutralized with a hydroxy-carboxylic acid, which is soluble in the polyol. The use of this hydroxy-carboxylic acid to neutralize the alkaline catalyst makes it possible to obtain a clear polyol product, which does need to be filtered before use and does not contribute to the generation of a filter cake requiring disposal. U.S. Pat. No. 4,430,490 is, however, limited to the production of polyether polyols from polyhydric alcohols such as sucrose.
U.S. Pat. No. 4,521,548 teaches that the alkaline catalyst used to produce the polyether polyols disclosed therein may be neutralized with formic acid. The benefit of neutralization with formic acid is also the solubility of the reaction product of the formic acid and alkaline catalyst in the product polyol.
Japanese Abstracts 57168917A and 57168918 each teach that neutralization of the alkaline catalyst used in the production of the amine-initiated polyethers disclosed therein may be achieved by the addition of oxalic acid in quantities sufficient to neutralize the alkaline catalyst. Some of the oxalate salts formed, however, are insoluble in the product polyol. After the catalyst is neutralized by oxalic acid, the product must be degassified to obtain the polyether polyol.
U.S. Pat. No. 4,877,879 teaches that neutralization of the alkaline catalyst used in the production of the amine-initiated polyethers disclosed therein may be achieved by adding formic acid in a substantial (i.e., greater than 300%) stoichiometric excess with respect to the amount of alkaline catalyst to be neutralized. The formic acid not only produces a salt, which is soluble in the product amine but also hydrogen, which is taught to contribute to the stability of the polyether.
U.S. Pat. No. 5,786,405 discloses a process for the production of a clear amine initiated polyether polyol by epoxidizing an amine in the presence of potassium hydroxide and upon completion of epoxidation, adding lactic acid to the epoxidized mixture in an amount sufficient to neutralize any remaining alkali metal hydride. It is beneficial to neutralize polyols with lactic acid because during neutralization, lactic acid produces a lactate salt, such as potassium lactate, which is soluble in the polyol and therefore does not require an additional process step to remove. However, the major problems observed with lactic acid neutralized polyols are the increased reactivity and high pressure during the polyurethane foam forming reaction. High reactivity results in insufficient flow and therefore incomplete filling of the cavities of the mold, while increased pressure can lead to deformation of the finished parts, particularly when foam is poured behind a thin shell, as in applications such as doors and water heaters.
Surprisingly, it has now been found that reducing the amount of catalyst used during the polyol synthesis and adding the catalyst earlier in the epoxidation reaction, gives, after lactic acid neutralization, a short chain polyol that has foam processing characteristics similar to the conventional sulfuric acid neutralized polyol.